Continuously variable headlamp control

ABSTRACT

A system for automatically controlling continuously variable headlamps on a controlled vehicle includes an imaging system capable of determining lateral and elevational locations of headlamps from oncoming vehicles and tail lamps from leading vehicles. The system also includes a control unit that can acquire an image from in front of the controlled vehicle. The image covers a glare area including points at which drivers of oncoming and leading vehicles would perceive the headlamps to cause excessive glare. The image is processed to determine if at least one oncoming or leading vehicle is within the glare area. If at least one vehicle is within the glare area, the headlamp illumination range is reduced. Otherwise, the illumination range is set to full illumination range.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 10/197,834, entitled “CONTINUOUSLY VARIABLE HEADLAMP CONTROL,”filed on Jul. 18, 2002, by Joseph S. Stam et al., which is acontinuation of U.S. patent application Ser. No. 09/938,774, entitled“CONTINUOUSLY VARIABLE HEADLAMP CONTROL,” filed on Aug. 24, 2001, byJoseph S. Stam et al., now U.S. Pat. No. 6,429,594, which is acontinuation of U.S. patent application Ser. No. 09/546,858, entitled“CONTINUOUSLY VARIABLE HEADLAMP CONTROL,” filed on Apr. 10, 2000, byJoseph S. Stam et al., now U.S. Pat. No. 6,281,632, which is acontinuation of U.S. patent application Ser. No. 09/157,063, entitled“CONTINUOUSLY VARIABLE HEADLAMP CONTROL,” filed on Sep. 18, 1998, byJoseph S. Stam et al., now U.S. Pat. No. 6,049,171. The entiredisclosure of each of the above-noted applications is incorporatedherein by reference. Priority under 35 U.S.C. §120 is hereby claimed tothe filing dates of each of the above-identified applications.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to automatically controllingcontinuously variable headlamps to prevent excessive glare seen bydrivers in front of the headlamps.

[0003] Recently, headlamps producing a continuously variableillumination range have become available. The illumination range may bevaried by one or both of changing the intensity of light and changingthe direction of light emitted by the headlamps.

[0004] Varying headlamp illumination intensity can be accomplished inseveral different means. A first means is to provide a pulse-widthmodulated (PWM) signal to the headlamp. By varying the duty cycle ofheadlamp power, the headlamp illumination intensity can be increased ordecreased. This may be accomplished by providing a PWM signal from acontrol system to a high power field effect transistor (FET) in serieswith the headlamp bulb.

[0005] Another means of varying the power duty cycle of a headlamp is toprovide a PWM signal to a lamp driver integrated circuit such as aMotorola MC33286. This integrated circuit provides the added advantageof limiting the maximum inrush current to the headlamp, thus potentiallyextending the life of the headlamp bulb.

[0006] Yet another means of varying headlamp illumination uses highintensity discharge (HID) headlamps. HID lamps are a new, highlyefficient headlamp technology. The ballasts used to power HID headlampscan be directly supplied with a control signal to vary headlampillumination intensity.

[0007] Still another means to vary the illumination intensity of aheadlamp is to provide an attenuating filter to absorb some of the lightemitted from the headlamp. An electrochromic filter may be placed infront of the headlamp. By controlling the voltage applied to theelectrochromic filter, the amount of light absorbed and, hence, theemitted illumination level, can be varied.

[0008] There are also several means available for changing the directionof light emitted from headlamps. Headlamp aim can be varied usingactuators to move the headlamp housing relative to the vehicle.Typically, these actuators are electric motors such as stepper motors.

[0009] For headlamps with appropriately designed reflectors,mechanically moving the light source relative to the reflector canchange headlamp beam direction as well as headlamp illuminationintensity.

[0010] HID headlamps provide several additional methods of aiming theheadlamp beam. Some of these methods involve deflecting or perturbingthe arc in such a way as to vary the lamp output. U.S. Pat. No.5,508,592 entitled “METHOD FOR DEFLECTING THE ARC OF AN ELECTRODELESSHID LAMP” to W. Lapatovich et al., which is hereby incorporated byreference, describes exciting the HID lamp with a high-frequency radiosignal. Modulating the signal causes the lamp to operate at an acousticresonance point, perturbing the arc from its quiescent position. Analternative technique, known as magnetodynamic positioning (MDP), uses amagnetic field to shape the HID arc. MDP is being developed by OsramSylvania Inc. of Danvers, Mass.

[0011] A collection of methods for implementing continuously variableheadlamps is described in Society of Automotive Engineers (SAE)publication SP-1323 entitled “Automotive Lighting Technology,” which ishereby incorporated by reference.

[0012] Automatic control of continuously variable headlamps offersseveral potential benefits over automatic control of traditional on-offheadlamps. Greater flexibility for illumination is available, allowingheadlamp illumination to be better adapted to driving conditions. Also,continuously varying the headlamp illumination does not create rapidchanges in illumination that may startle the driver. Various methodshave been devised to control both continuously variable and conventionaldiscrete headlamps. One of the oldest methods is to aim the headlamp inthe same direction as steered wheels. Another method increases theillumination range in proportion to increasing vehicle speed.

[0013] Still another method of controlling headlamps has been developedfor HID lamps. The increased brightness and bluish color of the HIDlamps is particularly disrupting to oncoming drivers. Due to thisdisruptness effect, certain European countries require headlamp levelingsystems if HID lamps are used on a vehicle. These headlamp levelingsystems detect the pitch of the vehicle relative to the road and adjustthe vertical aim of the headlamps accordingly. Advanced systems furtheruse the speed of the vehicle to anticipate small pitch disturbancescaused by acceleration.

[0014] One problem with current continuously variable headlamp controlsystems is the inability to consider oncoming or leading vehicles indetermining the illumination range of headlamps. One prior art device isexpressed in U.S. Pat. No. 4,967,319 entitled “HEADLIGHT APPARATUS FORAUTOMOTIVE VEHICLE” by Y. Seko. This device utilizes vehicle speed alongwith the output from a five-element linear optical sensor array directlycoupled to a headlamp. The headlamp incorporates motor drives to adjustthe elevational angle of illumination beams. This design requires aseparate sensing and control system for each headlamp or suggests as analternative a controlled headlamp only on the side of the vehicle facingopposing traffic. This design presents many problems. First, the opticalsensor and associated electronics are in close proximity to the hotheadlamp. Second, placing the image sensor on the lower front portion ofthe vehicle may result in imaging surfaces being coated with dirt anddebris. Third, placing the image sensor close to the headlamp beam makesthe system subject to the masking effects of scattered light from fog,snow, rain, or dust particles in the air. Fourth, this system has nocolor discriminating capability and, with only five pixels ofresolution, the imaging system is incapable of accurately determininglateral and elevational locations of headlamps or tail lights at anydistance.

[0015] What is needed is control of continuously variable headlampsbased on detection of oncoming headlamps and leading tail lights atdistances where headlamp illumination would create excessive glare forthe drivers of oncoming and leading vehicles.

SUMMARY OF THE INVENTION

[0016] The present invention may control continuously variable headlampsbased on detected headlamps from oncoming vehicles and tail lights fromleading vehicles. The control system may determine the proper aim ofheadlamps in steerable headlamp systems and may determine the properintensity of headlamps in variable intensity headlamp systems. Gradualchanges in the region of headlamp illumination may be supported. Thecontrol system also operates correctly over a wide range of ambientlighting conditions.

[0017] The headlamp control system of the present invention maydetermine the proper aim of headlamps in steerable headlamp systems.

[0018] The headlamp control system of the present invention may vary theintensity of headlamp beams continuously in response to detectedoncoming and leading vehicles.

[0019] The headlamp control system of the present invention may operatesuch that the transition from high beam to low beam or from low beam tohigh beam is gradual and thus not startling to the vehicle driver.

[0020] The present invention also provides control of continuouslyvariable headlamps over a wide range of ambient lighting conditions.

[0021] In carrying out the above objects and features of the presentinvention, a method for controlling continuously variable headlamps isprovided. The method includes detecting an ambient light level. Thecontinuously variable headlamps are set to daylight mode if the ambientlight level is greater than a first threshold. The headlamps are set tolow beam mode if the ambient light level is less than the firstthreshold but greater than a second threshold. Automatic headlampdimming is enabled if the ambient light level is less than the secondthreshold.

[0022] In an embodiment of the present invention, automatic headlampdimming includes obtaining an image in front of the headlamps. The imagecovers a glare area including points at which a driver in a vehicle infront of the headlamps would perceive the continuously variableheadlamps as causing excessive glare if the headlamps were at fullrange. The image is processed to determine if the vehicle is within theglare area. If the vehicle is within the glare area, the continuouslyvariable headlamp illumination range is reduced. Otherwise, thecontinuously variable headlamps are set to full illumination range. Invarious refinements, the continuously variable illumination range may bemodified by changing the intensity of light emitted, by changing thedirection of light emitted, or both.

[0023] In another embodiment of the present invention, reducing thecontinuously variable headlamp illumination range includes incrementallydecreasing the illumination range. Obtaining the image, processing theimage, and incrementally decreasing illumination range are repeateduntil the illumination range produces a level of illumination at theoncoming or leading vehicle position that would not be perceived ascausing excessive glare by the driver in the vehicle in front of thecontinuously variable headlamps.

[0024] In still another embodiment of the present invention, the ambientlight level is determined by a multipixel image sensor having anelevational angle relative to the controlled vehicle having continuouslyvariable headlamps. The method includes acquiring a sequence of images,finding a stationary light source in each image, calculating a measureof elevation for the stationary light source in each image, anddetermining the elevational angle based on the calculated measures ofelevation.

[0025] In a further embodiment of the present invention, the fullillumination range is reduced if at least one form of precipitation,such as fog, rain, snow, and the like, is detected.

[0026] In a still further embodiment of the present invention, eachcontinuously variable headlamp has an effective illumination rangevaried by changing vertical direction aimed. Each effective illuminationrange has an elevational direction corresponding to an upper extent ofthe headlamp beam bright portion. The method further includes acquiringa sequence of images. The elevational direction is determined for atleast one continuously variable headlamp in each image of the sequence.A determination is then made as to whether or not the sequence of imageswas taken during travel over a relatively straight, uniform surface. Ifso, the determined elevational directions are averaged to obtain anestimate of actual elevational direction.

[0027] A system for controlling at least one continuously variableheadlamp on a controlled vehicle is also provided. Each continuouslyvariable headlamp has an effective illumination range varied by changingat least one parameter from a set including horizontal direction aimed,vertical direction aimed, and intensity emitted. The system includes animaging system capable of determining lateral and elevational locationsof headlamps from oncoming vehicles and tail lamps from leadingvehicles. The system also includes a control unit that can acquire animage from in front of the at least one headlamp. The image covers aglare area including points at which the driver of a vehicle in front ofthe headlamps would perceive the headlamps as causing excessive glare.The image is processed to determine if at least one vehicle includingoncoming vehicles and leading vehicles is within the glare area. If atleast one vehicle is within the glare area, the headlamp illuminationrange is reduced. Otherwise, the headlamp illumination range is set tofull illumination range.

[0028] In an embodiment of the present invention, the controlled vehiclehas at least one low beam headlamp with variable intensity and at leastone high beam headlamp with variable intensity. The control unit reducesthe illumination range by decreasing the intensity of the high beamheadlamp while increasing the intensity of the low beam headlamp.

[0029] In another embodiment of the present invention wherein headlampsproduce illumination through heating at least one filament, the controlunit causes a low amount of current to flow through each filament whenthe controlled vehicle engine is running and when the headlampcontaining the filament is not controlled to emit light. The low amountof current heating the filament decreases filament brittleness therebyprolonging filament life.

[0030] In still another embodiment of the present invention, the imagingsystem is incorporated into the rearview mirror mount. The imagingsystem is aimed through a portion of the controlled vehicle windshieldcleaned by a windshield wiper.

[0031] In yet another embodiment of the present invention, thecontrolled vehicle has a headlamp with a variable vertical aimdirection. The system further includes at least one sensor fordetermining vehicle pitch relative to the road surface. The control unitaims the headlamp to compensate for controlled vehicle pitch variations.In a refinement, the controlled vehicle includes a speed sensor. Thecontrol unit anticipates controlled vehicle pitch changes based onchanges in controlled vehicle speed.

[0032] In a further embodiment of the present invention, the controlledvehicle includes headlamps with variable horizontal aim direction. Thecontrol unit determines if a leading vehicle is in a curb lane on theopposite side of the controlled vehicle from oncoming traffic and is inthe glare area. If no leading vehicle is in one of the curb lanes,headlamp illumination range is reduced by aiming the headlamps away fromthe direction of oncoming traffic.

[0033] In a still further embodiment of the present invention, thecontrol unit reduces headlamp illumination range at a predetermined rateover a predetermined transition time.

[0034] A system is also provided for controlling at least onecontinuously variable headlamp having an effective illumination rangevaried by changing vertical direction aimed. Each effective illuminationrange has an elevational direction corresponding to an upper extent ofthe headlamp beam bright portion. The system includes an imaging systemcapable of determining lateral and elevational locations of headlampsfrom oncoming vehicles. The imaging system is mounted a verticaldistance above each headlamp. The system also includes a control unitfor acquiring an image in front of the headlamps. The image covers aglare area including points at which the driver of the oncoming vehiclewould perceive the continuously variable headlamps to cause excessiveglare. The image is processed to determine if at least one oncomingvehicle is within the glare area. If at least oncoming vehicle is withinthe glare area, the elevational angle between the imaging system and theheadlamps of each of the at least one oncoming vehicles is determined.If at least one oncoming vehicle is within the glare area, thecontinuously variable headlamps are aimed such that the elevationaldirection is substantially parallel with a line between the imagingsystem and the headlamps of the oncoming vehicle producing the greatestof the determined elevational angles.

[0035] A system is further provided for controlling continuouslyvariable headlamps. The system includes at least one moisture sensor fordetecting at least one form of precipitation such as fog, rain, andsnow. The system also includes a control unit to reduce the headlampfull illumination range when precipitation is detected.

[0036] These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In the drawings:

[0038]FIG. 1 is a diagram showing a continuously variable headlampillumination range together with oncoming and leading vehicles;

[0039]FIG. 2 is a block diagram of a control system according to anembodiment of the present invention;

[0040]FIG. 3 is a flow diagram of a method for controlling continuouslyvariable headlamps in different ambient lighting conditions according tothe present invention;

[0041]FIG. 4 is a flow diagram of automatic headlamp dimming accordingto the present invention;

[0042]FIG. 5 is a flow chart of a method for detecting tail lampsaccording to an embodiment of the present invention;

[0043]FIG. 6 is a flow chart of a method for detecting headlampsaccording to an embodiment of the present invention;

[0044]FIG. 7 is a schematic diagram illustrating reduction of headlampillumination range according to an embodiment of the present invention;

[0045]FIG. 8 is a flow diagram of an alternative method for reducingheadlamp illumination range according to the present invention;

[0046]FIG. 9 is an illustration of street lamp imaging according to thepresent invention;

[0047]FIGS. 10a and 10 b are schematic diagrams of apparent street lightelevational angle as a function of camera-to-vehicle inclination angle;

[0048]FIG. 11 is a schematic diagram illustrating street lampelevational angle calculation according to an embodiment of the presentinvention;

[0049]FIG. 12 is a graph illustrating street lamp elevational angles forthree different camera-to-vehicle inclination angles;

[0050]FIG. 13 is a flow diagram of a method for calculatingcamera-to-vehicle inclination angle according to an embodiment of thepresent invention;

[0051]FIG. 14 is an imaging system that may be used to implement thepresent invention;

[0052]FIG. 15 is a schematic diagram of image array sensor subwindowsthat may be used to implement the present invention;

[0053]FIG. 16 is a schematic diagram of an embodiment of an image arraysensor that may be used to implement the present invention;

[0054]FIGS. 17a through 17 e are schematic diagrams of an embodiment ofthe present invention;

[0055]FIG. 18 is a block diagram illustrating registers and associatedlogic used to control the image control sensor according to anembodiment of the present invention;

[0056]FIG. 19 is a timing diagram illustrating image array sensorcontrol signals for the logic in FIG. 18;

[0057]FIG. 20 is an ambient light sensor that may be used to implementthe present invention;

[0058]FIG. 21 is a diagram illustrating mounting of a moisture sensorthat may be used to implement the present invention; and

[0059]FIG. 22 is a diagram illustrating operation of a moisture sensorthat may be used to implement the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] Referring now to FIG. 1, a continuously variable headlampillumination range together with oncoming and leading vehicles is shown.Controlled vehicle 20 includes at least one continuously variableheadlamp 22. Each headlamp 22 produces a variable region of bright lightknown as illumination range 24. A driver in oncoming vehicle 26 orleading vehicle 28 that is within illumination range 24 may viewheadlamps as producing excessive glare. This glare may make it difficultfor the driver of oncoming vehicle 26 or leading vehicle 28 to seeobjects on the road, to read vehicle instruments, and to readjust tonight viewing conditions once vehicle 26, 28 is outside of illuminationrange 24. Hence, illumination range 24 is perceived as a glare area bythe driver of oncoming vehicle 26 or leading vehicle 28.

[0061] The present invention attempts to reduce the level of glare seenby the driver of oncoming vehicle 26 or leading vehicle 28 by providinga control system that detects oncoming vehicle 26 or leading vehicle 28and reduces illumination range 24 accordingly.

[0062] Referring now to FIG. 2, a block diagram of a control systemaccording to an embodiment of the present invention is shown. A controlsystem for continuously variable headlamps, shown generally by 40,includes imaging system 42, control unit 44, and at least onecontinuously variable headlamp system 46. Imaging system 42 includesvehicle imaging lens system 48 operative to focus light 50 from a regiongenerally in front of controlled vehicle 20 onto image array sensor 52.Imaging system 42 is capable of determining lateral and elevationallocations of headlamps from oncoming vehicles 26 and leading vehicles28. In a preferred embodiment of the present invention, vehicle imaginglens system 48 includes two lens systems, one lens system having a redfilter and one lens system having a cyan filter. Lens system 48 permitsimage array sensor 52 to simultaneously view a red image and a cyanimage of the same region in front of controlled vehicle 20. Image arraysensor 52 is preferably comprised of an array of pixel sensors. Furtherdetails regarding vehicle imaging lens system 48 and image array sensor52 are described with regards to FIGS. 14 through 16 below.

[0063] In a preferred embodiment, imaging system 42 includes ambientlight lens system 54 operable to gather light 56 over a wide range ofelevational angles for viewing by a portion of image array sensor 52.Ambient light lens system 54 is described with regards to FIG. 20 below.Alternatively, light 50 focused through vehicle imaging lens system 48may be used to determine ambient light levels. Alternatively, a lightsensor completely separate from imaging system 42 may be used todetermine ambient light levels.

[0064] In a preferred embodiment, imaging system 42 is incorporated intothe interior rearview mirror mount. Imaging system 42 is aimed through aportion of the windshield of controlled vehicle 20 cleaned by at leastone windshield wiper.

[0065] Control unit 44 accepts pixel gray scale levels 58 and generatesimage sensor control signals 60 and headlamp illumination controlsignals 62. Control unit 44 includes imaging array control andanalog-to-digital converter (ADC) 64 and processor 66. Processor 66receives digitized image data from and sends control information toimaging array control and ADC 64 via serial link 68. A preferredembodiment for control unit 44 is described with regards to FIGS. 17through 19 below.

[0066] Control system 40 may include vehicle pitch sensors 70 to detectthe pitch angle of controlled vehicle 20 relative to the road surface.Typically, two vehicle pitch sensors 70 are required. Each sensor ismounted on the chassis of controlled vehicle 20 near the front or rearaxle. A sensor element is fixed to the axle. As the axle moves relativeto the chassis, sensor 70 measures either rotational or lineardisplacement. To provide additional information, control unit 44 mayalso be connected to vehicle speed sensor 72.

[0067] Control system 40 may include one or more moisture sensors 74.Precipitation, such as fog, rain, or snow, may cause excessive lightfrom headlamps 22 to be reflected back to the driver of controlledvehicle 20. Precipitation may also decrease the range at which oncomingvehicles 26 and leading vehicles 28 may be detected. Input from moisturesensor 74 may therefore be used to decrease the full range ofillumination range 24. A moisture sensor that may be used to implementthe present invention is described with regards to FIGS. 21 and 22below.

[0068] Each continuously variable headlamp 22 is controlled by at leastone headlamp controller 76. Each headlamp controller 76 accepts headlampillumination control signals 62 from control unit 44 and affectsheadlamp 22 accordingly to modify illumination range 24 of light 78leaving headlamp 22. Depending on the type of continuously variableheadlamp 22 used, headlamp controller 76 may vary the intensity of light78 leaving headlamp 22, may vary the direction of light 78 leavingheadlamp 22, or both. Examples of circuits that may be used for headlampcontroller 76 are described with regards to FIGS. 17d and 17 e below.

[0069] In one embodiment of the present invention, control unit 44 canacquire an image covering a glare area including points at which adriver of oncoming vehicle 26 or leading vehicle 28 would perceiveheadlamps 22 to cause excessive glare. Control unit 44 processes theimage to determine if at least one vehicle 26, 28 is within the glarearea. If at least one vehicle is within the glare area, control unit 44reduces illumination range 24. Otherwise, headlamps 22 are set to fullillumination range 24.

[0070] In a preferred embodiment of the present invention, reductions toillumination range 24 and setting headlamps 22 to full illuminationrange 24 occurs gradually. Sharp transitions in illumination range 24may startle the driver of controlled vehicle 20 since the driver may notbe aware of the precise switching time. A transition time of between oneand two seconds is desired for returning to full illumination range 24from dimmed illumination range 24 corresponding to low beam headlamps.Such soft transitions in illumination range 24 also allow control system40 to recover from a false detection of oncoming vehicle 26 or leadingvehicle 28. Since image acquisition time is approximately 30 ms,correction may occur without the driver of controlled vehicle 20noticing any change.

[0071] For controlled vehicle 20 with both high beam and low beamheadlamps 22, reducing illumination range 24 may be accomplished bydecreasing the intensity of high beam headlamps 22 while increasing theintensity of low beam headlamps 22. Alternately, low beam headlamps canbe left on continuously when ambient light levels fall below a certainthreshold.

[0072] For controlled vehicle 20 with at least one headlamp 22 having avariable horizontal aimed direction, the aim of headlamp 22 may be movedaway from the direction of oncoming vehicle 26 when illumination range24 is reduced. This allows the driver of controlled vehicle 22 to bettersee the edge of the road, road signs, pedestrians, animals, and the likethat may be on the curb side of controlled vehicle 22. In a preferredembodiment, control unit 44 may determine if any leading vehicle 28 isin a curb lane on the opposite side of controlled vehicle 20 fromoncoming traffic and is in the glare area. If not, reducing illuminationrange 24 includes aiming headlamps 22 away from the direction ofoncoming traffic. If a leading vehicle is detected in a curb lane,illumination range 24 is reduced without changing the horizontal aim ofheadlamps 22.

[0073] Referring now to FIG. 3, a flow diagram of a method forcontrolling continuously variable headlamps in different ambientlighting conditions according to the present invention is shown. ForFIG. 3 and for each additional flow diagram shown, operations are notnecessarily sequential operations. Similarly, operations may beperformed by software, hardware, or a combination of both. The presentinvention transcends any particular implementation and aspects are shownin sequential flow chart form for ease of illustration.

[0074] During twilight, different drivers or automated headlamp systemswill turn on headlamps and running lights at different times. Since thepresent invention relies on detecting headlamps of oncoming vehicles 26and tail lamps of leading vehicles 28, there may be a period of timebetween when controlled vehicle 20 has headlamps turned on and whenvehicles 26, 28 can be detected. To accommodate various ambient lightconditions at which headlamps and tail lamps of vehicles 26, 28 may beturned on, an embodiment of the present invention uses two thresholdsfor system operation.

[0075] The ambient light level is detected in block 90. In block 92, theambient light level is compared to a day threshold. When the ambientlight level is greater than the day threshold, headlamps are set todaylight mode in block 94. Daylight mode may include turning on daylightrunning lamps (DRLs).

[0076] In an embodiment of the present invention wherein the controlledvehicle includes headlamps, such as continuously variable headlamps 22,which produce illumination by heating at least one filament, theeffective filament life may be extended by causing a low amount ofcurrent to flow through the element when the headlamp is not controlledto emit light. The amount of current is large enough to heat thefilament without causing the filament to emit light. This heating makesthe filament less brittle and, hence, less susceptible to shock andvibration damage.

[0077] When ambient light levels fall below the day threshold, theambient light level is compared to the night threshold in block 96. Ifthe ambient light level is less than the day threshold but greater thanthe night threshold, headlamps are set to low beam mode in block 98. Inlow beam mode, either standard low beam headlamps may be turned on orcontinuously variable headlamps 22 may be set to an illumination range24 corresponding to a low beam pattern. Running lights including taillamps may also be turned on.

[0078] When ambient light levels fall below the night threshold level,automatic headlamp dimming is enabled in block 100. During automaticheadlamp dimming mode, control unit 44 acquires an image in front ofheadlamps 22. The image covers the glare area including points at whichthe drivers of oncoming vehicles 26 or leading vehicles 28 wouldperceive headlamps 22 to cause excessive glare. Control unit 44processes the image to determine if any vehicles 26, 28 are within theglare area. If at least one vehicle 26, 28 is within the glare area,control unit 44 reduces headlamp illumination range 24. Otherwise,headlamp illumination range 24 is set to full illumination range.

[0079] Several benefits, in addition to reducing glare seen by driversof oncoming vehicles 26 and leading vehicles 28, are achieved by thepresent invention. Studies have shown that many drivers rarely use highbeams either out of fear of forgetting to dim the high beams, out ofunfamiliarity with high beam controls, or due to preoccupation withother aspects of driving. By automatically providing the full range ofillumination when oncoming vehicles 26 and leading vehicles 28 are notpresent, the driver of controlled vehicle 20 will experience greatervisibility.

[0080] Another benefit achieved by the present invention is the abilityto illuminate areas in front of controlled vehicle 20 currently notlegally permitted.

[0081] Current limitations on high beam aiming are based, in part, onnot completely blinding the drivers of oncoming vehicles 26 if the highbeams are not dimmed. Using control system 40, illumination range 24 maybe expanded to better illuminate overhead and roadside signs, greatlyaiding in night navigation. Because the present invention automaticallydecreases illumination range 24 due to an approaching oncoming vehicle26 or leading vehicle 28, the risk of temporarily blinding the driver ofvehicles 26, 28 is greatly reduced.

[0082] Referring now to FIG. 4, a flow diagram of automatic headlampdimming according to the present invention is shown. The methodsdescribed in FIGS. 4 through 6 are more fully described in U.S. Pat. No.5,837,994 entitled “CONTROL SYSTEM TO AUTOMATICALLY DIM VEHICLE HEADLAMPS” by Joseph S. Stam et al., the entire disclosure of which ishereby incorporated by reference.

[0083] Control unit 44 is used to acquire and examine images obtainedthrough imaging system 42 to detect the presence of vehicles 26, 28. Animage is acquired through the cyan filter in block 110. A loop, governedby block 112, selects the next pixel to be processed. The next pixel isprocessed in block 114 to detect the presence of headlamps. A method fordetecting the presence of headlamps is described with regards to FIG. 6below. A check is made to determine if any headlamps for oncomingvehicles 26 are found in block 116. Generally, headlamps of oncomingvehicles 26 appear much brighter than tail lamps of leading vehicles 28.Hence, the gain for images used to search for tail lamps is greater thanthe gain used to search for headlamp images. Therefore, headlamps ofoncoming vehicles 26 appearing in an image used to search for tail lampsmay wash out the image. If no headlamps are found, images are acquiredthrough cyan and red filters in block 118. A loop, governed by block120, is used to select each image pixel through the red filter andcorresponding image pixel through the cyan filter. Each red image pixeland corresponding cyan image pixel are processed in block 122 to detectthe presence of tail lamps. A method that may be used to detect taillamps using red and cyan image pixels is described with regards to FIG.5 below. Once the check for headlamps is completed and, if no headlampsare detected, the check for tail lamps is completed, the illuminationrange is controlled in block 124. Various alternatives for controllingillumination range 24 of continuously variable headlamps 22 aredescribed with regards to FIGS. 2 and 3 above and to FIGS. 7 through 13below.

[0084] Alternatives to the method shown in FIG. 4 are possible. Forexample, the image obtained through the cyan filter in block 110 may beused as the image obtained through the cyan filter in block 116.

[0085] Referring now to FIG. 5, a flow chart of a method for detectingtail lamps according to an embodiment of the present invention is shown.Pixels in image array sensor 52 that image light 50 through the redfilter in vehicle imaging lens system 48 are examined.

[0086] The location of each pixel within image array sensor 52 is firstdetermined to be within the tail lamp window in block 130. In apreferred embodiment of the present invention, image array sensor 52contains more pixels than are necessary to acquire an image through thered and cyan filters having sufficient resolution. These additionalpixels can be used to compensate for imperfections in aiming imagingsystem 42 relative to controlled vehicle 20. By including additionalrows and columns of pixels, rows and columns of pixels on the edge ofimage array sensor 52 may be disregarded to compensate for aimingvariations. Methods for aiming imaging system 42 relative to controlledvehicle 20 will be described with regards to FIGS. 9 through 13 below.If the pixel is not determined to be within the tail lamp window, theflow diagram is exited and the next pixel is selected for examination asin block 132.

[0087] If the pixel selected from the red image is within the tail lampwindow, the value of the pixel is compared to the corresponding pixelfrom the cyan image in block 134. A decision is made in block 136 basedon the comparison. If the red pixel is not N% greater than the cyanpixel, the next red pixel is determined as in block 132. Severalcriteria may be used to determine the value of N. N may be fixed. N mayalso be derived from the ambient light level. N may further be based onthe spatial location of the examined pixel. Distant leading vehicle 28in front of controlled vehicle 20 may be subjected to illumination 24 atfull range intensity. Thus, a lower value for N may be used for pixelsdirectly in front of controlled vehicle 20 while a higher value for Nmay be used for pixels corresponding to areas not directly in front ofcontrolled vehicle 20.

[0088] Once the examined pixel is determined to be sufficiently red, oneor more brightness thresholds are determined in block 138. The intensityof the red pixel is then compared to the one or more thresholds in block140. If the examined red pixel is not sufficiently bright enough, thenext pixel to be examined is determined as in block 132. The one or morethresholds may be based on a variety of factors. A threshold may bebased on the average illumination level of surrounding pixels. It mayalso be based on settings for image array sensor 52 and ADC 64. Theaverage pixel intensity over the entire image may also be used to set athreshold. As in the case of N, the threshold may also be determined bythe pixel spatial location. For example, the threshold for pixelsoutside of 6° right and left of center should correspond to a lightlevel incident on image array sensor 52 of about 12 times as bright asthe threshold of red light directly in front of controlled vehicle 20and pixels between a 3° and 6° lateral angle should have a light levelabout 4 times as bright as a pixel imaged in front of controlled vehicle20. Such spatial varying thresholds help to eliminate false tail lampdetection caused by red reflectors along the side of the road.

[0089] Once the examined pixel is determined to be sufficiently red anddetermined to have a sufficient illumination level, the pixel is addedto a tail lamp list in block 142. Pixels are filtered for reflectorrecognition in block 144. The position of each pixel in the tail lamplist is compared to the position of pixels in the tail lamp lists fromprevious images to determine if the pixels represent tail lamps orroadside reflectors. Several techniques may be used. First, rapidrightward motion of a pixel over several frames is a strong indicationthat the pixels are imaging a stationary reflector. Also, since thespeed at which controlled vehicle 20 overtakes leading vehicle 28 ismuch less than the speed at which controlled vehicle 20 would overtake astationary reflector, the rate of increase in brightness of pixels wouldbe typically much greater for a stationary reflector than for tail lampson leading vehicle 28. A decision is made in block 46 to determine ifthe pixel is a reflector image. If not, a determination is made that atail lamp has been detected in block 148.

[0090] Referring now to FIG. 6, a flow chart of a method for detectingheadlamps according to an embodiment of the present invention is shown.A pixel from image array sensor 52 is selected from a region viewinglight 50 through vehicle image lens system 48 having a cyan filter. Thepixel to be examined is first checked to determine if the pixel iswithin the headlamp window in block 160. As in block 130 in FIG. 5above, block 160 permits corrections in the aiming of imaging system 42by not using all rows and columns of image array sensor 52. If theexamined pixel is not within the headlamp window, the flow chart isexited and the next pixel is obtained as in block 162.

[0091] A check is made in block 164 to determine if the examined pixelis greater than an upper limit. If so, a determination is made that aheadlamp has been detected in block 166 and the flow chart is exited.The upper limit used may be a fixed value, may be based on the ambientlight level, and may also be based on the spatial location of theexamined pixel.

[0092] If the upper limit in intensity is not exceeded, one or morethresholds are calculated in block 168. A comparison is made in block170 to determine if the intensity of the examined pixel is greater thanat least one threshold. If not, the next pixel to be examined isdetermined in block 162. As in block 138 in FIG. 5 above, the one ormore thresholds may be determined based on a variety of factors. Theambient light level may be used. Also, the average intensity of pixelssurrounding the examined pixel may be used. Further, the vertical andhorizontal spatial location of the examined pixel may be used todetermine the threshold.

[0093] If the examined pixel is greater than at least one threshold, thepixel is added to the headlamp list in block 172. Each pixel in theheadlamp list is filtered for recognition as a street lamp in block 174.One filtering method that may be used is to examine a sequence of pixelsin successive frames corresponding to a potential headlamp. If thislight source exhibits alternating current (AC) modulation, the lightsource is deemed to be a street lamp and not a headlamp. Another methodthat may be used is the relative position of the light source inquestion from frame to frame. If the light source exhibits rapidvertical movement, it may be deemed a street lamp. A determination ismade in block 176 as to whether or not the light source is a streetlamp. If the light source is not a street lamp, a decision is made thata headlamp has been detected in block 178.

[0094] Referring to FIG. 7, a schematic diagram illustrating reducingheadlamp illumination range according to an embodiment of the presentinvention is shown. Controlled vehicle 20 has continuously variableheadlamp 22 with adjustable elevational aim. Imaging system 42 ismounted in the rearview mirror mounting bracket and aimed to lookthrough the windshield of controlled vehicle 20. In this position,imaging system 42 is approximately 0.5 meters above the plane ofcontinuously variable headlamps 22. When oncoming vehicle 26 isdetected, an angle is calculated between the direction of vehicleforward motion 190 and the headlamps of oncoming vehicle 26. Thisinclination angle 192 is used to aim continuously variable headlamps 22.The elevational direction of the upper extent of illumination range 24,indicated by 194, is set to be approximately parallel with a line fromimaging system 42 to the headlamps of oncoming vehicle 26. This placesbeam upper extent 194 approximately 0.5 meters below the headlamps ofoncoming vehicle 26, thereby providing aiming tolerance, lighting theroad nearly to oncoming vehicle 26, and avoiding striking the eyes ofthe driver of oncoming vehicle 26. If multiple vehicles 26 are detected,beam upper extent 194 is set to be substantially parallel with thegreatest of the determined elevational angles 192.

[0095] In an embodiment, the adjustment range of continuously variableheadlamps 22 may be restricted, particularly when angle 192 issubstantially above or below a normal level. When one or more vehiclepitch sensors 70 are also used, control system 40 may base the aiming ofheadlamps 22 on output from imaging system 42 when lamps of oncomingvehicles 26 or leading vehicles 28 have been located and levelingcontrol may be used otherwise. In yet another embodiment, input fromvehicle pitch sensors 70 may be used to calculate a limit on how high toset beam upper extent 194 to keep the beam elevation within regulatedranges. Inputs from vehicle speed sensor 72 may be used to anticipateacceleration of controlled vehicle 20 to maintain the proper inclinationfor beam upper extent 194.

[0096] Referring now to FIG. 8, a flow diagram of an alternative methodfor reducing headlamp illumination range according to the presentinvention is shown. An image is acquired in block 200 and adetermination is made to see if any vehicle is within the glare area inblock 202. Techniques for determining the presence of oncoming vehicle26 or leading vehicle 28 have been described with regards to FIGS. 4through 6 above. If no vehicle is detected, the illumination range isset to full range in block 204.

[0097] If a vehicle is detected within the glare area, the illuminationrange is decreased incrementally in block 206. This results inillumination range 24 being decreased at a predetermined rate over apredetermined transition time. Several techniques are available fordecreasing illumination range 24. First, the intensity of light emittedby continuously variable headlamp 22 may be decreased. Second, headlamps22 may be aimed downward. Third, headlamps 22 may be aimed horizontallyaway from the direction of oncoming vehicle 26. In a refinement of thelast option, a check is made to determine if any leading vehicles 28 arein curb lanes on the opposite side of controlled vehicle 20 fromoncoming vehicle 26. If any leading vehicles 28 are detected,continuously variable headlamps 22 are not aimed toward the curb lane.The rate at which illumination range 24 is decreased may be constant ormay be a function of parameters including the current inclination angleof continuously variable headlamps 22, the estimated range of oncomingvehicle 26 or leading vehicle 28, ambient light levels, and the like.

[0098] Depending on the automatic headlamp dimming technique used,precise measurements of camera-to-vehicle and headlamp-to-camera anglesmay be required. Concerning the latter, the difference between thedirection that control system 40 commands of the beam of continuouslyvariable headlamp 22 versus the actual direction of the beam of headlamp22 relative to imaging system 42 is a critical system parameter. Forexample, low beams are designed to provide a very sharp transition froma relatively strong beam with beam upper extent 194 projected about 1.5°downward to a greatly diminished intensity which is normally viewed bydrivers of vehicles 26, 28 in the path of the beams. Thus, errors of0.5°, particularly in the elevational direction, are significant. Errorsof 2° are likely to subject drivers of vehicles 26, 28 to intolerableglare from direct, prolonged exposure to brighter portions ofillumination range 24 as if headlamp 22 had not been dimmed at all. Theposition of illumination range 24 relative to imaging system 42 may bedetermined using control system 40.

[0099] In one embodiment, the position of illumination range 24 issensed directly relative to the lights of oncoming vehicles 26 andleading vehicles 28 as adjustments to illumination range 24 are beingmade. In an alternative embodiment, illumination range 24 is momentarilydelayed from returning to full range. A sequence of images is takencontaining beam upper extent 194. If controlled vehicle 20 is in motionand the beam pattern stays the same in each of the sequence of images,control vehicle 20 can be assumed to be moving on a straight and levelroad. Beam upper extent 194 can then be determined relative to imagingsystem 42 by looking for a sharp transition between very bright and verydim regions in the output of image array sensor 52. The intensity ofillumination range 24 may also be varied during the sequence of imagesto ensure that the bright-to-dim transition is actually caused bycontinuously variable headlamp 22. Experimentation is required todetermine a reasonable minimum speed, length of time, and number offrames to obtain satisfactorily consistent measurements for a particularimplementation.

[0100] A method for aiming imaging system 42 relative to controlledvehicle 20 is to precisely position controlled vehicle 20 in front of atarget that can be seen by imaging system 42. This method is ideallysuited to the automobile manufacturing process where aiming imagingsystem 42 may be incorporated with or replace current headlamp aiming.Vehicle dealerships and repair shops may be equipped with a similartargeting apparatus.

[0101] Referring now to FIGS. 9 through 13, a method for establishingthe aim of imaging system 42 relative to controlled vehicle 20 that maybe performed during the normal operation of controlled vehicle 20 isdescribed. This method may be used in conjunction with the targetingmethod described above.

[0102] Referring now to FIG. 9, an illustration of street lamp imagingis shown. Image 220 represents an output from imaging system 42 showinghow street lamp 222 might appear in a sequence of frames. By notingchanges in the relative position of street lamp 222 in image 220, thevertical and horizontal aim of imaging system 42 relative to controlledvehicle 20 forward motion can be determined. For simplicity, thefollowing discussion concentrates on determining vertical angle. Thisdiscussion can be extended to determining horizontal angle as well.

[0103] Referring now to FIGS. 10a and 10 b, schematic diagrams ofapparent street light elevational angle as a function ofcamera-to-vehicle inclination angle are shown. In FIG. 10a, imagingsystem axis 230 is aligned with vehicle forward motion direction 190.Imaging system axis 230 can be thought of as a normal to the plane ofimage array sensor 52. Over a sequence of images, street lamp 222appears to be approaching imaging system 42. The angle between streetlamp 222 and imaging system axis 230, shown by 232, increases linearly.

[0104] In FIG. 10b, imaging system 42 is not aimed in the direction ofvehicle forward motion 190. In particular, vehicle forward motiondirection 190 and imaging system axis 230 form inclination angle 234.Therefore, in a sequence of images, street lamp elevational angle 232appears to increase in a non-linear fashion.

[0105] Referring now to FIG. 11, a schematic diagram illustrating streetlamp elevational angle calculation according to an embodiment of thepresent invention is shown. Image array sensor 52 in imaging system 42is represented as an array of pixels, one of which is shown by 240. Thenumber of pixels 240 shown in FIG. 11 is greatly reduced for clarity.Vehicle imaging lens system 48 is represented by single lens 242. Streetlamp 222 is imaged by lens 242 onto image array sensor 52 as street lampimage 244. Street lamp elevational angle 232, shown as θ, can becalculated by equation 1:${\tan (\theta)} = \left( \frac{\left. {{IRN} - {RRN}} \right) \cdot {PH}}{FL} \right)$

[0106] where RRN (Reference Row Number) is the row number correspondingto imaging system axis 230, IRN (Image Row Number) is the row number ofstreet lamp image 244, PH is the row height of each pixel 240, and FL isthe focal length of lens 242 relative to image array sensor 52.

[0107] Referring now to FIG. 12, a graph illustrating street lampelevational angles for three different camera-to-vehicle inclinationangles is shown. Curves 250, 252, 254 show the cotangent of theinclination angle as a function of simulated distance for street lamp222 that is five meters high. Images are taken at 20 meter intervalsfrom 200 to 80 meters as controlled vehicle 20 approaches street lamp222. For curve 250, imaging system axis 230 is aligned with vehicleforward motion direction 190. For curve 252, imaging system axis 230 is0.5° above vehicle forward motion direction 190. For curve 254, imagingsystem axis 230 is 0.5° below vehicle forward motion direction 190.Curve 250 forms a straight line whereas curve 252 is concave upward andcurve 254 is concave downward.

[0108] Referring now to FIG. 13, a flow diagram of a method forcalculating camera-to-vehicle inclination angle according to anembodiment of the present invention is shown. A count of the number ofimages taken is reset in block 260. The image count is compared to themaximum count (max count) required in block 262. The number of imagesrequired should be determined experimentally based on the type ofimaging system 42 used and the configuration of imaging system 42 incontrolled vehicle 22. If the image count is less than the maximumcount, the next image is acquired and the image count is incremented inblock 264.

[0109] A light source is found in the image in block 266. If this is thefirst image in a sequence or if no suitable light source has beenpreviously found, a number of light sources may be marked for potentialconsideration. If a light source has been found in a previous image inthe sequence, an attempt is made to find the new position of that lightsource. This attempt may be based on searching pixels in the last knownlocation of the light source and, if a sequence of positions is known,may be based on extrapolating from the sequence of light source imagesto predict the next location of the light source.

[0110] A check is made to determine if the light source is stationary inblock 268. One check is to determine if the light source exhibits ACmodulation by examining light source intensity over successive images.Another check is to track the relative position of the light source inthe sequence of images. If the light source is not stationary, the imagecount is reset in block 270. If the light source is stationary, anelevational measure is calculated in block 272. A technique forcalculating elevational angle was described with regards to FIG. 11above.

[0111] When each image in a sequence of max count images contains astationary light source, elevational measurements are validated in block274. As indicated with regards to FIG. 12 above, a sequence ofelevational measurements for a stationary light source, when expressedas the cotangent of the angle as a function of distance, forms either astraight line, a concave upward curve, or a concave downward curve. Thesequence of elevational measurements is examined to ensure that thesequence fits one of these patterns. If not, the sequence is discardedand a new sequence is obtained.

[0112] In an embodiment of the present invention, a check is made todetermine if the sequence of images was acquired during relativelysteady travel at a relatively constant speed. If not, the sequence isdiscarded and a new sequence is obtained. Constant speed can be checkedusing the output of speed sensor 72. Steady travel may be checked byexamining the relative positions of stationary and non-stationary lightsources over a sequence of frames.

[0113] The image elevation relative to the vehicle is determined inblock 276. If the sequence of elevational measurements does not form astraight line, inclination angle 234 may be estimated by adding aconstant value representing the radiant value correction to each of thetangent values to arrive at a corrected tangent value. The reciprocalsof the new values are taken and analyzed to determine the differencebetween successive values. If the difference is zero, the correctionvalue is the tangent of inclination angle 234. If the sequence ofdifferences is not zero, the concavity of the new sequence isdetermined. If the concavity direction of the new sequence is the sameas the original sequence, the correction value is increased. If theconcavity directions are opposite, the correction factor is decreased. Anew sequence of differences is then obtained and the process isrepeated.

[0114] Referring now to FIG. 14, a cross-sectional drawing of an imagingsystem that may be used to implement the present invention is shown. Asimilar imaging system is more completely described in U.S. Pat. No.6,130,421, entitled “IMAGING SYSTEM FOR VEHICLE HEADLAMP CONTROL” by JonH. Bechtel et al., the entire disclosure of which is hereby incorporatedby reference. Imaging system 42 includes housing 280 which holds vehicleimaging lens system 48 and image array sensor 52. Housing 280 definesaperture 282 which opens onto a scene generally in front of controlledvehicle 20. Support 284 serves to hold red lens 286 and cyan lens 288and serves to prevent light coming through aperture 282 and not passingthrough a lens 286, 288 from striking image array sensor 52. As isfurther described with regards to FIG. 15 below, image array sensor 52has a first region for receiving light transmitted by red lens 286 and asecond, non-overlapping region for receiving light transmitted by cyanlens 288. Aperture 282, the spacing between lenses 286, 288, and baffle290 are designed to minimize the amount of light passing through one oflens 286, 288 and striking the portion of image sensor 52 used to imagelight from the other of lens 286, 288.

[0115] An embodiment of lenses 286, 288 will now be described. Lenses286, 288 may be manufactured on a single plate of polymer, such asacrylic, shown as 292. The polymer may optionally include infraredfiltration, ultraviolet filtration, or both. Each lens 286, 288 isplano-convex with the forward facing surface convex and aspheric. Thefront surface of each lens 286, 288 may be described by equation 2:$Z = \frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}}$

[0116] where Z is the value of the height of the lens surface along theoptical surface as a function of the radial distance r from the opticalaxis, c is the curvature, and k is the conic constant. For the frontsurface of red lens 286, c equals 0.456 mm⁻¹ and k equals −1.0. For thefront surface of cyan lens 288, c equals 0.446 mm⁻¹ and k equals −1.0.Lenses 286, 288 have a diameter of 1.1 mm and have centers spaced 1.2 mmapart. At the center, each lens 286, 288 is 1.0 mm. Plate 292 is mountedto baffle 284 such that the back of each lens 286, 288 is 4.0 mm infront of image array sensor 52. This distance is indicated by focallength FL in FIG. 14. Red and cyan filters are printed onto the rearflat surfaces of red lens 286 and cyan 288, respectively, using screen,pad, or other printing techniques. The red filter substantiallytransmits light of wavelengths longer than 625 nm while attenuatinglight of wavelength shorter than 625 nm. The cyan filter substantiallytransmits light of wavelength shorter than 625 nm while attenuatinglight of wavelength longer than 625 nm. The preferable field of viewafforded by lenses 286 and 288 is 10° high by 20° wide.

[0117] Referring now to FIG. 15, a schematic diagram of image arraysensor subwindows that may be used to implement the present inventionare shown. Image array sensor 52 includes an array of pixel sensors, oneof which is indicated by 240, arranged in rows and columns. Image arraysensor 52 includes top border 302, bottom border 304, left border 306,and right border 308 defining a region covered by pixel sensors 240.Image array sensor 52 is divided into several subwindows. Uppersubwindow 310 is bounded by borders 308, 312, 314, and 316, and containspixel sensors 240 struck by an image projected through red lens 286.Lower subwindow 318 is bounded by borders 308, 320, 314, and 322, andincludes pixel sensors 240 onto which an image is projected through cyanlens 288.

[0118] Lenses 286, 288 provide a field of view in front of controlledvehicle 20 such as, for example, 22° wide by 9° high. A space betweenborder 312 and top edge 302 and between borders 316 and 324 allow for anelevational adjustment to correct for misalignment of imaging system 42in controlled vehicle 20. To accomplish the adjustment, upper subwindow310, defined by borders 312 and 316, are moved up or down within therange between top edge 302 and border 324. Similarly, borders 320 and322 represent boundaries for lower subwindow 318 that may be movedbetween bottom edge 304 and border 326. Pixel sensors 240 that liewithin the region between borders 324 and 326 may receive light fromboth red lens 286 and cyan lens 288. Therefore, this region is notnormally used as part of the active imaging area. Although onlyelevational adjustment has been described, lateral adjustment is alsopossible.

[0119] Pixel sensors 240 lying between left edge 306 and border 314 maybe used for ambient light sensing. Ambient light sensing is describedwith regards to FIG. 20 below.

[0120] In a preferred embodiment of the present invention, image arraysensor 52 includes a 256×256 array of square pixel sensors 240. In analternative embodiment, pixel sensor 52 includes a 256×128 square arrayof rectangular pixels, resulting in a vertical resolution greater thanthe horizontal resolution.

[0121] Referring now to FIG. 16, a schematic diagram of an embodiment ofan image array sensor that may be used to implement the presentinvention is shown. Pixel sensor 240 and the technique for correlateddouble sampling shown are described in U.S. Pat. No. 5,471,515 entitled“ACTIVE PIXEL SENSOR WITH INTRA-PIXEL CHARGE TRANSFER” to E. Fossum etal., which is hereby incorporated by reference. The circuitry describedcan be built using standard CMOS processes. Devices similar to imagearray sensor 52 are available from Photobit Corporation of Pasedena,Calif.

[0122] Image sensor array 52 includes an array of pixels 240. Lightstriking photogate transistor 330 in each pixel 240 generates electricalcharge which is accumulated beneath photogate transistor 330. Duringcharge collection, the gate of photogate transistor 330 is held at apositive voltage to create a well beneath photogate transistor 330 tohold the accumulated charge. The gate of gate electrode 332 is held at aless positive voltage, V_(TX), to form a barrier to the flow ofelectrons accumulated beneath photogate transistor 330. In anembodiment, V_(TX) is 3.8 volts relative to VSS. When charge readout isdesired, the gate of photogate transistor 330 is brought to a voltageless than V_(TX). The accumulated charge then flows from photogatetransistor 330 through gate electrode 332 to the region beneath floatingdiffusion 334. Floating diffusion 334 is connected to the gate ofn-channel FET 336 which has its drain connected to supply voltage VDD.Typically, VDD is 5.0 volts referenced to VSS. The gate of photogatetransistor 330 is returned to its original voltage. A potentialproportional to the accumulated charge can now be sensed at the sourceof FET 336.

[0123] During charge transfer and readout, the gate of reset electrode338 is held at a low positive voltage to form a barrier to electrodesbeneath floating diffusion 334. When the gate of reset electrode 338 isbrought to a high positive voltage, charge collected beneath floatingdiffusion 334 is transferred through the region beneath reset electrode338 and into drain diffusion 340 which is connected to VDD. This bringsthe source of FET 336 to an initial or reset potential. By subtractingthis reset potential from the illumination potential proportional toaccumulated charge, a great degree of fixed pattern noise may beeliminated. This technique is known as correlated double sampling.

[0124] Pixel sensors 240 are arranged in rows and columns. In apreferred embodiment, all of the pixels in a row of a selected subwindoware read simultaneously into readout circuits, one of which is indicatedby 342. One readout circuit 342 exists for each column. The row to beread is selected by a row address, indicated generally by 344. Rowaddress 344 is fed into row decoder 346 causing the row select line 348corresponding to row address 344 to become asserted. When row selectline 348 is asserted, n-channel FET 350 is turned on, allowing thepotential at the source of FET 336 to appear on column readout line 352.All pixels 240 in each column are connected to a common column readoutline 352. However, since each pixel in the column has a unique rowaddress, only one row select line 348 can be asserted resulting in atmost one FET 336 source potential appearing on column readout line 352.

[0125] Two control signals provide the timing for gating charge in eachpixel 240. Photogate signal (PG) 354 is a high asserting signalindicating when charge is to be transferred from photogate transistor330 to floating diffusion 334. Each row has a gate 356 which ANDs PGsignal 354 and row select line 348 to produce row PG signal 358 which isconnected to the gate of each photogate transistor 330 in the row. Rowreset signal (RR) 360 is a high asserting signal indicating whenfloating diffusions 334 should be returned to the reset potential. Eachrow has gate 362 which ANDs RR signal 360 with the appropriate rowselect line 348 to produce reset signal 364 which is connected to thegate of each reset electrode 338 in the row.

[0126] Voltages at the source of FET 336 are dropped across load FET 366when FET 350 is on. Load FET 366 is an n-channel device with a fixedgate voltage of V_(LN). In this embodiment, V_(LN) is approximately 1.5volts referenced to VSS. Each pixel 240 may contain load FET 366 or, asis shown in FIG. 16, one load FET 366 may be used for each column.

[0127] Readout circuit 342 provides sample-and-hold for potentials oncolumn readout line 352 as well as output buffering. Two input signalscontrol each readout circuit 342. Sample-and-hold reset signal (SHR) 368turns on n-channel FET 370 allowing the potential on column readout line352 to charge capacitor 372. Capacitor 372 is used to store the resetpotential. Sample-and-hold illumination signal (SHS) 374 turns onn-channel FET 376. This permits the potential on column readout line 352to charge capacitor 378. Capacitor 378 is used to hold the illuminationpotential proportional to the charge accumulated by photogate transistor330.

[0128] At the end of a complete readout operation, the reset potentialand illumination potential from each pixel 240 in a selected row arestored in capacitors 372, 378 in each readout circuit 342. A columnaddress, shown generally by 380, is input into decoder 382 assertingcorresponding column select line 384. Each column select line 384controls an associated readout circuit 342 to determine which readoutcircuit 342 will be driving common output lines SIGOUT 386 holding theillumination potential and RSTOUT 388 holding the reset potential.Buffer 390, with input connected across capacitor 378 and outputconnected to SIGOUT 386, and buffer 392, with input connected acrosscapacitor 372 and output connected to RSTOUT 388 in each readout circuit342 are enabled by the appropriate column select line 384.

[0129] Referring now to FIGS. 17a through 17 e, a schematic diagram ofan embodiment of the present invention is shown. Much of the circuitryshown in FIGS. 17a and 17 b is described in U.S. Pat. No. 5,990,469,entitled “CONTROL CIRCUIT FOR IMAGE ARRAY SENSORS,” to Jon H. Bechtel etal., the entire disclosure of which is hereby incorporated by reference.

[0130] In FIG. 17a, image array sensor 52 is shown as integrated circuitchip U7. Biasing circuitry 400 is used to set the various voltagelevels, such as V_(TX) and V_(LN), required by image array sensor 52.Output SIGOUT 386 and RSTOUT 388 are the illumination potential andreset potential respectively for pixel 240 selected by row address 344and column address 380.

[0131] Difference amplifier 402, such as the AD 830 High Speed, VideoDifference Amplifier by Analog Devices, accepts SIGOUT 386 and RSTOUT388 and produces noise-reduced signal 404. ADC 406, such as LTC 1196 byLinear Technology, accepts noise-reduced signal 404 and producesdigitized signal (ADDATA) 408. The analog-to-digital conversion isstarted by asserting conversion signal (CONVST) 410. The converted valueis serially shifted out at a rate determined by the input ADC clocksignal (ADCLK) 412.

[0132] The integrated circuit designated U4 and associated componentsregulate the approximately 12-volt car battery output to a 5-volt VCCsupply voltage. The integrated circuit U3 and associated componentsproduce a conditioned 5-volt supply signal.

[0133] In FIG. 17b, application specific integrated circuit (ASIC) 414is shown. ASIC 414 contains much of the logic for controlling imagearray sensor 52 and ADC 406 as well as for communicating with processor66. In the embodiment shown, ASIC 414 is an XC4003E from Xylinx.However, it is well known in the art that a wide range of means areavailable for implementing the logic in ASIC 414 including discretelogic, custom VLSI integrated circuits, various FPGAs, programmablesignal processors, and microcontrollers. The logic implemented by ASIC414 is described with regards to FIG. 18 below. Serial memory 416, suchas the AT17C65 by Atmel, is configured to store and automaticallydownload the code describing the designed logical operation into ASIC414 each time power is first applied. Clock signal 418, labeled OSC, isgenerated by processor 66 and drives the sequential logic in ASIC 414.

[0134] ASIC 414 communicates with processor 66 using three lines. Datais shifted serially between ASIC 414 and processor 66 on master outslave in (MOSI) 420 at a rate determined by serial peripheral serialclock (SPSCLK) 422 in a direction determined by slave select (SSI) 424.When SSI 424 is asserted, processor 66 is the master and ASIC 414 is theslave. Processor 66 shifts instruction words into ASIC 414. In thismode, processor 66 drives SPSCLK 422. During instruction execution,processor 66 deasserts SSI 424 making ASIC 414 the master and processor66 the slave. ASIC 414 shifts digitized, noise reduced intensity signalsto processor 66. In this mode, ASIC 414 generates SPSCLK 422.

[0135] As technology improves, it is desirable to locate image arraysensor 52, difference amplifier 402, ADC 406, and the logic implementedin ASIC 414 on a single integrated circuit chip. It may be possible toinclude processor 66 on such a chip as well.

[0136] In FIG. 17c, processor 66 and associated electronics are shown.Processor 66 may be an H8S2128 microcontroller from Hitachi. Processor66 generates instructions for ASIC 414 that determine, in part, whichsubwindows of image array sensor 52 will be examined. Processor 66receives digitized intensities from each pixel 240 in designatedsubwindows of image array sensor 62. Processor 66 uses these intensitiesto carry out the methods described with regards to FIGS. 3 through 13above for controlling continuously variable headlamps 22. One necessaryfunction is control of the gain for images acquired using image arraysensor 52. As described with regards to FIG. 4 above, the gain for animage used to detect the tail lamps of leading vehicles 28 needs to begreater than the gain for an image used to detect headlamps of oncomingvehicles 26. One or more of several means are possible for controllingimage array sensor 52 gain. First, the integration time of pixels 240can be varied. Second, the reference voltage, VREF, of ADC 406 can bechanged. Third, difference amplifier 402 can have a variable,controllable gain. Fourth, a variable aperture or a variable attenuator,such as an electrochromic window, can be placed in the path of lightstriking image array sensor 52.

[0137] The types and numbers of control signals required for headlamps22 depend on headlamp configuration in controlled vehicle 20. For theembodiment described below, controlled vehicle 20 has two continuouslyvariable high beam headlamps 22 and two continuously variable low beamheadlamps 22. Each high beam headlamp 22 can be vertically andhorizontally aimed using stepper motors. The intensity of both high beamheadlamps 22 is controlled by a single PWM signal. The two low beamheadlamps 22 are not steerable but have intensities controlled by asingle PWM signal. It is apparent to one of ordinary skill in the artthat the present invention can control various configurations ofcontinuously variable headlamps 22.

[0138] Processor 66 includes a first set of control signals, showngenerally by 426, for controlling the aim of the left high beamheadlamp. A similar set of eight control signals, shown generally by428, are used to control the aim of the right high beam headlamp. Labelshave been left off right aim control signals 428 for clarity. Adescription of aim control signals 426, 428 is provided with regard toFIG. 17e below. Processor 66 also generates high beam modulated signal430 which is buffered to become high beam PWM signal 432. Identicalcircuitry may be connected to low beam modulated signal 434. Thiscircuitry has been omitted for clarity. Headlamp controller 76 using PWMsignal 432 is described with regards to FIG. 17d below.

[0139] In FIG. 17d, headlamp system 46 includes incandescent headlamp 22and headlamp intensity controller 76. Headlamp intensity controller 76includes a power FET, such as the IRFZ44N by International Rectifier.The intensity of light emitted by headlamp 22 is proportional to theduty cycle of PWM signal 432. A base frequency for PWM signal 432 of2000 Hz is preferred. Higher frequencies may increase the powerdissipation of the power FET.

[0140] In FIG. 17e, headlamp system 46 includes headlamp 22 withvariable vertical and horizontal aiming and headlamp controller 76 forproviding aiming signals. Headlamp 22 includes vertical stepper motor440 for controlling vertical aim direction and horizontal stepper motor442 for controlling horizontal aim direction. Headlamp 22 also includesvertical home switch 444 and horizontal home switch 446 for indicatingwhen headlamp 22 is in the home position. Vertical home switch 444produces vertical home signal (VSW) 448. Horizontal home switch 446produces horizontal home signal (HSW) 450. Vertical motor 440 is drivenby motor controller 452, such as the SAA1042 by Motorola. Motorcontroller 452 has three inputs. Vertical direction (VDIR) 454 indicatesthe direction of rotation of motor 440 for each positive edge onvertical clock (VCLK) 456. Vertical step (VSTEP) indicates whether motor440 will make a full step or a half step for each applied pulse of VCLK456. Horizontal motor controller 460 has horizontal direction (HDIR)462, horizontal clock (HCLK) 464, and horizontal step (HSTEP) 466 whichfunction similar to VDIR 454, VCLK 456, and VSTEP 458 for vertical motorcontroller 452.

[0141] In an alternative embodiment using HID headlamps, the directionof light emitted from one or more headlamps 22 is changed using MDP. HIDheadlamps operate by producing a charged arc in a gas such as xenon. Thearc may be perturbed by the presence of a magnetic field. Reflectors maybe designed such that various perturbations of the arc produce changesin the direction, intensity, or both of light emitted by HID headlamp22.

[0142] Aim control signals 426, 428 from processor 66 may be replaced byanalog or digital outputs determining the direction for aiming theoutput of HID headlamp 22. Headlamps utilizing MDP are being developedby Osram Sylvania Inc. of Danvers, Mass.

[0143] Referring now to FIG. 18, a block diagram illustrating registersand associated logic used to control the image control sensor is shown.The logic described below is more completely discussed in U.S. Pat. No.5,950,469, entitled “CONTROL CIRCUIT FOR IMAGE ARRAY SENSORS,” to Jon H.Bechtel et al., the entire disclosure of which is hereby incorporated byreference.

[0144] ASIC 414 includes control logic 480 which controls a collectionof registers and associated logic. All but two of the registers areinitially loaded with data from an instruction serially shifted overMOSI 420 from processor 66. The path used to initialize the registers,indicated by 482, is shown as a dashed line in FIG. 18. The purpose foreach of the registers and associated logic will now be described.

[0145] ASIC 414 can specify two subwindows within image array sensor 52.The first subwindow is specified by low and high column addresses andlow and high row addresses. The second subwindow is specified as havinga column offset and a row offset from the first subwindow. Hence, thefirst and second subwindows have the same size. These two subwindows maybe upper subwindow 310 and lower subwindow 318 described with regard toFIG. 15 above. As described with regards to FIG. 16 above, readout andreset of each pixel 240 occurs by rows. Alternate rows from eachsubwindow are obtained. Each pixel in the selected row of firstsubwindow is read and then each pixel in the selected row of the secondsubwindow is read.

[0146] Five registers are used to specify column address 380. Secondsubwindow column offset register (SCO) 484 holds the column offsetbetween the first subwindow and the second subwindow. Low columnregister (LC) 486 holds the starting column value for the firstsubwindow. High column register (HC) 488 holds the ending column valueof the first subwindow. Active column register (AC) 490 holds the valueof the currently examined column in the first subwindow. Column selectregister (CS) 492 holds column address 380. Multiplexer 494 is initiallyset so that register AC 490 is loaded with the same column startingvalue as register LC 486 when processor 66 shifts an instruction intoASIC 414. During instruction execution, multiplexer 496 is initially setso that register CS 492 is loaded with the value of register AC 490.Register AC 490 is incremented to select each column in the firstsubwindow until the content of register AC 490 is greater than the finalcolumn value in register HC 488 as determined by comparator 498.Register AC 490 is then reloaded with the starting column value fromregister LC 486 through multiplexer 494. Multiplexer 496 is then set sothat register CS 492 is loaded with the sum of register AC 490 andregister SCO 484 produced by adder 499. As register AC 490 isincremented, register CS 492 then holds successive column addresses 380of the second subwindow.

[0147] Row address 344 is specified using six registers. Secondsubwindow row offset register (SRO) 500 holds the row offset between thefirst subwindow and the second subwindow. Low row register (LR) 502holds the starting row address of the first subwindow. High row register(HR) 504 holds the ending row address of the first subwindow. RR 506holds the address of the first subwindow row for reset. ADC row register(AR) 508 holds the first subwindow row to be read out foranalog-to-digital conversion. Row select register (RS) 510 holds rowaddress 344. Register RR 506 and register AR 508 are used to determinethe integration time for each pixel 240. If each row in image arraysensor 52 is reset immediately prior to readout, a very shortintegration time results. If each row is reset immediately followingreadout, a longer integration period results, the length of whichdepends on the number of rows in the first subwindow. An additionalmeans for further extending integration time is described below. Fourrows must therefore be considered, the reset row of the first subwindow,the reset row of the second subwindow, the conversion row of the firstsubwindow, and the conversion row of the second subwindow. Multiplexer512 and multiplexer 514 are first set to pass the contents of registerRR 506 into register RS 510. This makes the reset row of the firstsubwindow row address 344. Multiplexers 512, 514 are then set so thatregister RS 510 is loaded with the sum of register RR 506 and registerSRO 500 produced by adder 516. This makes row address 344 the reset rowof the second subwindow. Multiplexers 512, 514 are then set to loadregister RS 510 with the contents of register AR 508. This makes rowaddress 344 the conversion row of the first subwindow. Multiplexers 512,514 are then set so that register RS 510 is loaded with the sum ofregister AR 508 and register SRO 500 produced by adder 516. This makesrow address 344 the conversion row of the second subwindow. Register RR506 and register AR 508 are then incremented. When the contents ofregister RR 506 are greater than the ending row value held in registerHR 504 as determined by comparator 518, register RR 506 is reloaded withthe starting row address of the first subwindow from register LR 502through multiplexer 520. When the value held in register AR 508 isgreater than the ending row address in register HR 504 as determined bycomparator 522, register AR 508 is loaded with the starting address ofthe first subwindow from register LR 502.

[0148] Two registers allow an integration period greater than the frameperiod, which is defined as the time required to convert each row in thefirst subwindow. Integration frame delay register (IFD) 524 holds thetwo's complement of the number of frame periods for each integrationperiod.

[0149] Integration frame counter register (IFC) 526 is initially loadedthrough multiplexer 528 with the value loaded into register IFD 524 plusone provided by serial incrementer 530. Incrementer 530 has an outputindicating overflow. If register IFD 524 is initialized with negativeone, incrementer 530 indicates an overflow. This overflow signalscontrol logic 480 to perform row readouts during the next frame period.If an overflow does not occur from incrementer 530, no row readout isperformed during the next frame period. At the end of each frame period,the contents of register IFC 526 are passed through incrementer 530 bymultiplexer 528 and incrementer 530 overflow is checked again. Whenoverflow occurs, multiplexer 528 gates the contents of register IFD 524through incrementer 530 into register IFC 526 and the process isrepeated.

[0150] Reset frame count register (RFC) 532 is initialized with thetwo's complement of the number of frames to be read plus one. This valueis used to indicate the number of times in which an instruction shiftedin from processor 66 is to be repeated. At the end of each frame inwhich all rows of the first and second subwindows have been read, theoverflow output of incrementer 534 is examined. If an overflow hasoccurred, the instruction is completed and no further processing occurs.If no overflow has occurred, the contents of register RFC 532 are passedthrough multiplexer 536 and incremented by incrementer 534.

[0151] Outputs from comparators 498, 518, 522 and incrementers 530, 534are used by control logic 480 to generate internal control signals formultiplexers 494, 496, 520, 512, 514, 528, 536 and incrementers forregisters 490, 506, 508 as well as for external control signals such asPG 354, RR 360, SHS 374, SHR 368, CONVST 410, and ADCLK 412.

[0152] Referring now to FIG. 19, a timing diagram illustrating imagearray sensor control signals is shown. The timing diagram is provided toshow timing relationships between signals and not necessarily precisetimes between signal events.

[0153] The beginning of the timing diagram in FIG. 19 corresponds withthe start of an instruction execution by ASIC 414. Row address (ROW) 344is first set to the starting row of the first subwindow, as shown by550. Signals RR 360 and PG 354 are then asserted dumping any charge thatmay be beneath photogate 330 in each pixel 240 in row 550, as showngenerally by 552. Row address 344 is then set to the first row of thesecond subwindow, as shown by 554. Again, signals RR 360 and PG 354 areasserted, as shown by 556, to reset all pixels 240 in second subwindowfirst row 554. Row address 344 is then set to the first subwindow secondrow, as shown by 558, and signals RR 360 and PG 354 are asserted asshown by 560. This process continues by alternately resetting the nextrow from the first subwindow then the corresponding row from the secondsubwindow.

[0154] At some point in the future, the time arrives to read the valuesfrom each pixel 240 in the first row of the first subwindow. Row address344 is again set to first subwindow first row address 550. Signal RR 360is asserted, as shown by 562, to dump any charge under floatingdiffusion 334. Next, signal SHR 564 is asserted to gate the resetpotential for each pixel 240 in first subwindow first row 550 intocapacitor 372 of corresponding column readout circuit 342. Next, signalPG 354 is asserted, as shown by 566, to transfer charge accumulatedunder photogates 330 to floating diffusions 334. Signal SHS 374 is thenasserted, as shown by 568, to gate the illumination potential for eachpixel 240 into capacitor 378 of corresponding column readout circuit342. Integration period 569 is the time between deasserting signal PG354 during reset 569 and asserting signal PG 354 during readout 566.

[0155] The conversion process for each column in first subwindow firstrow 550 can now begin. Column address (COL) 380 is set to first windowfirst column, as shown by 570. Signal CONVST 410 is then asserted at572. This causes ADC 406 to begin conversion. ASIC 414 provides asequence of clock pulses on ADCLK 412 and receives the digitizedillumination value serially on ADDATA 408. ASIC 414 immediately shiftsthe data to processor 66 over MOSI 420 as shown by 574. In the exampleshown in FIG. 19, each subwindow contains only four columns. Theaddresses for first subwindow second column 576, third column 578, andfourth column 580 are successively used as column address 380, and theconversion process is repeated.

[0156] Row address 344 can then be set to second subwindow first row 554and the sequence of assertions for signals RR 360, SHR 368, PG 354, andSHS 374 repeated to load column readout circuits 342 with reset andillumination potentials. Column address 380 can be set to secondsubwindow first column 382 and the conversion sequence can be repeated.

[0157] Note that, since the conversion process uses reset andillumination potentials stored in readout circuits 342 and columnaddress 380 but not row address 344 and that row reset requires rowaddress 344 but not column address 380 or readout circuits 342, rowreset may be interleaved with the conversion process. This is seen inFIG. 19 where, following assertion of SHS signal 374 at 568, row address344 is set to the first subwindow n^(th) row address 584 and signals RR360 and PG 354 are asserted at 586 to reset all pixels 240 in firstsubwindow n^(th) row 584.

[0158] Referring now to FIG. 20, an ambient light sensor that may beused to implement the present invention is shown. The ambient lightsensor may be incorporated into imaging system 42. The ambient lightsensor is described more fully in U.S. Pat. No. 6,130,421, entitled“IMAGING SYSTEM FOR VEHICLE HEADLAMP CONTROL,” to Jon H. Bechtel et al.,the entire disclosure of which is hereby incorporated by reference.

[0159] Ambient light lens system 54 includes baffle 600 built onto thefront of housing 280. Baffle 600 is angled at an angle θ ofapproximately 45° with the horizontal of controlled vehicle 20. Baffle600 defines aperture 602 opening towards the front of controlled vehicle20. Aperture 602 may be trapezoidal such that the projection of aperture602 onto a vertical surface would form a rectangle on the verticalsurface. Lens 604 is mounted in one side of aperture 602. The width oflens 604 is approximately the same as the diameter of red lens 286 orcyan lens 288. Lens 604 accepts light rays over a wide elevationalrange, such as vertical ray 606 and horizontal ray 608, and directsthese rays into an approximately horizontal direction. Lens 604 ispositioned so that a blurred, inverted image of lens 604 is projected byred lens 286 onto one edge of image array sensor 52 between top border302 and border 316 to form red sky image 610. Lens 604 is alsopositioned so that a blurred, inverted image of lens 604 is projected bycyan lens 288 between bottom border 304 and border 320 to form cyan skyimage 612. The active length of lens 604 is made short enough to permitthe entire active length to be projected onto red sky image 610 and cyansky image 612.

[0160] Red sky image 610 and cyan sky image 612 are examined inprocessor 66 to determine an ambient light level. The intensity valuesmay be averaged to determine ambient light levels. Lens 604 may bedesigned so that light 56 from different ranges of elevational anglesappears in different regions of lens 604. In this case, light levelsfrom different ranges of elevational angles may be weighted higher thanfrom other ranges of elevation angles when an average is determined. Forexample, near vertical light may be weighted highest and near horizontallight may be weighted lowest. Also, since red sky image 610 and cyan skyimage 612 are correlated, intensities as a function of color may beobtained. For example, the effective ambient light level may beincreased for a blue sky as compared with a cloudy sky.

[0161] Referring now to FIG. 21, a diagram illustrating mounting of amoisture sensor that may be used to implement the present invention isshown. Moisture sensor 74, as well as imaging system 42, may beconstructed into mounting bracket 620 of interior rearview mirror 622.Moisture sensor 74 may be mounted two to three inches behind windshield624 of controlled vehicle 20.

[0162] Referring now to FIG. 22, a diagram illustrating operation of amoisture sensor that may be used to implement the present invention isshown. Moisture sensor 74 and associated control system are described inU.S. Pat. No. 5,923,027, entitled “MOISTURE SENSOR AND WINDSHIELD FOGDETECTOR,” by Joseph S. Stam et al., which is hereby incorporated byreference.

[0163] Moisture sensor 74 includes image array sensor 630, lens 632, andlight source 634. Lens 632 is designed to focus windshield 624 ontoimage array sensor 630. Moisture sensor 74 operates in two modes, onefor detecting droplets on windshield 624 and one for detecting fog onwindshield 624. The first mode uses the focusing effect of a droplet ofwater. When windshield 624 is dry, the scene appearing on image arraysensor 630 will be blurred since the scene has an effective focal lengthof infinity and lens 632 is focused on windshield 624. If droplets ofwater due to precipitation, such as rain or snow, are present onwindshield 624, portions of the scene viewed by image array sensor 630will be more sharply focused. Since an unfocused scene has less highfrequency spatial components than a sharply focused scene, examining theoutput of image array sensor 630 for high spatial frequency componentswill provide an indication of droplets on windshield 624. In the secondoperating mode, light source 634 shines a beam of light, shown generallyby 636, onto windshield 624. If no fog is present on windshield 624,beam 636 will pass through windshield 624 and will not be seen by imagearray sensor 630. If fog is present on the interior of window 624, beam636 will be reflected as interior light spot 638 which will be detectedby image array sensor 630. Likewise, if fog is on the exterior but notthe interior of window 624, beam 636 will be reflected as exterior lightspot 640 which will be seen by image array sensor 630. If light spot638, 640 is seen by image array 630, the relative height of light spot638, 640 in the image can be used to determine whether the fog is on theinterior or exterior of windshield 624.

[0164] Image array sensor 630 may be similar in construction to imagearray sensor 52. However, the number of pixels required for image arraysensor 630 is significantly less than for image array sensor 52. A 64×64array of pixels is considered to be appropriate for image array sensor630. The angle of windshield 624 in current passenger cars is about 27°.Such a configuration may cause raindrops and other moisture to be atdifferent distances from the image sensor depending on where themoisture is on windshield 624. To help compensate for this problem, thetop of image array sensor 630 may be angled approximately 10° towardwindshield 624.

[0165] In a preferred embodiment, lens 632 is a single biconvex lenshaving a 6 mm diameter, front and rear radius of curvature of 7 mm foreach surface, and a center thickness of 2.5 mm. The front surface oflens 632 may be positioned 62 mm from the outer surface of windshield624. Mounting bracket 620 may form a stop of about 5 mm directly infront of lens 632. Image array sensor 630 may be located about 8.55 mmfrom the rear surface of lens 632.

[0166] Light source 634 is preferably a light emitting diode (LED).Light source 634 either emits highly collimated light or, as in theembodiment shown in FIG. 22, lens 642 is used to focus the light fromlight source 634 onto windshield 624. Light source 634 may emit visiblelight or, preferably, infrared light so as not to create a distractionfor the driver of the controlled vehicle 20. Light source 634 may bepositioned a few millimeters above lens 632 and angled so that beam 636strikes windshield 624 in an area imaged by image array sensor 630.

[0167] The output from image array sensor 630 must be processed in amanner similar to the output of image array sensor 52. A separate imagearray control and ADC, similar to control and ADC 64, and processor,similar to processor 66, may be provided for this purpose. Alternately,a separate imaging array control and ADC may be used with processor 66.A further embodiment is to use the same control unit 44 for the outputof both image array sensor 52 and moisture sensor 74. Processor 66 wouldcontrol which image array sensor 52, 630 was being examined.

[0168] The above description is considered that of the preferredembodiments only. Modifications of the invention will occur to thoseskilled in the art and to those who make or use the invention.Therefore, it is understood that the embodiments shown in the drawingsand described above are merely for illustrative purposes and notintended to limit the scope of the invention, which is defined by thefollowing claims as interpreted according to the principles of patentlaw, including the doctrine of equivalents.

The invention claimed is:
 1. An automatic exterior light control,comprising: an image array sensor, said image array sensor comprising anarray of pixel sensors; and a controller configured to generate anexterior light control signal, said controller is further configured togenerate a rate of change of said exterior light control signal that isa function of one of the variables selected from the group comprising: acurrent inclination angle of a headlight, an estimated range of anoncoming vehicle, an estimated range of a leading vehicle and an ambientlight level.
 2. An automatic exterior light control as in claim 1wherein said exterior light control signal is an intensity signal.
 3. Anautomatic exterior light control as in claim 1 wherein said exteriorlight control signal is a horizontal direction signal.
 4. An automaticexterior light control as in claim 1 wherein said exterior light controlsignal is a vertical direction signal.
 5. An automatic exterior lightcontrol, comprising: an image array sensor, said image array sensor isconfigured to sense at least one illumination range and at least oneother vehicle; and a controller, said controller is configured togenerate a continuously variable exterior light control signal as afunction of said illumination range and said at least one other vehicle.6. An automatic exterior light control as in claim 5 wherein said atleast one illumination range is of a continuously variable headlight ofa controlled vehicle.
 7. An automatic exterior light control as in claim6 wherein said headlight is a low beam headlight.
 8. An automaticexterior light control as in claim 6 wherein said headlight is a highbeam headlight.
 9. An automatic exterior light control as in claim 5wherein said at least one other vehicle is at least one oncomingvehicle.
 10. An automatic exterior light control as in claim 5 whereinsaid at least one other vehicle is at least one leading vehicle.
 11. Anautomatic exterior light control as in claim 5 wherein said imager isconfigured to sense said at least one illumination range as said atleast one illumination range is being adjusted.
 12. An automaticexterior light control as in claim 5 wherein said imager and saidcontroller are configured to provide a positive feedback to insure thatsaid at least one illumination range is as desired.
 13. An automaticexterior light control as in claim 5 wherein said at least one sensedillumination range sensed is an upper vertical limit.
 14. An automaticexterior light control as in claim 5 wherein said at least one sensedillumination range is an outer lateral limit.
 15. An automatic exteriorlight control as in claim 5 wherein said at least one sensedillumination range is an intensity.
 16. An automatic exterior lightcontrol, comprising: an image array sensor, said image array sensor isconfigured to sense at least one illumination range; and a controller,said controller is configured to generate a continuously variableexterior light control signal as a function of said illumination range.17. An automatic exterior light control as in claim 16 wherein said atleast one illumination range is of a continuously variable headlight ofa controlled vehicle.
 18. An automatic exterior light control as inclaim 17 wherein said headlight is a low beam headlight.
 19. Anautomatic exterior light control as in claim 17 wherein said headlightis a high beam headlight.
 20. An automatic exterior light control as inclaim 16 wherein said imager is configured to sense said at least oneillumination range as said at least one illumination range is beingadjusted.
 21. An automatic exterior light control as in claim 16 whereinsaid imager and said controller are configured to provide a positivefeedback to insure that said at least one illumination range is asdesired.
 22. An automatic exterior light control as in claim 16 whereinsaid at least one sensed illumination range sensed is an upper verticallimit.
 23. An automatic exterior light control as in claim 16 whereinsaid at least one sensed illumination range is an outer lateral limit.24. An automatic exterior light control as in claim 16 wherein said atleast one sensed illumination range is an intensity.
 25. An automaticexterior light control, comprising: an image array sensor configured todetect at least one image, said image array sensor comprising an aim;and a controller, said controller is configured to generate acontinuously variable exterior light control signal, said controller isfurther configured to automatically calibrate said aim of said imagearray sensor relative to a controlled vehicle as a function of said atleast one detected image.
 26. An automatic exterior light control as inclaim 25 wherein said controller automatically calibrates said aim ofsaid image array sensor when the controlled vehicle is positioned infront of a target that can be seen by said image array sensor.
 27. Anautomatic exterior light control as in claim 25 wherein said controllerautomatically calibrates said aim of said image array sensor by sensingchanges in a relative position of street lamps in said at least onedetected image.
 28. An automatic exterior light control, comprising: animage array sensor, said image array sensor comprising an array of pixelsensors; and a controller configured to generate an exterior lightcontrol signal, said controller is further configured to generate a rateof change of said exterior light control signal that is a function ofthe brightness of at least one detected light source.
 29. An automaticexterior light control as in claim 28 wherein said exterior lightcontrol signal is an intensity signal.
 30. An automatic exterior lightcontrol as in claim 28 wherein said exterior light control signal is ahorizontal direction signal.
 31. An automatic exterior light control asin claim 28 wherein said exterior light control signal is a verticaldirection signal.
 32. An automatic exterior light control, comprising:an image array sensor, said image array sensor comprising an array ofpixel sensors; and a controller configured to generate an exterior lightcontrol signal, said controller is further configured to generate a rateof change of said exterior light control signal that is not a functionof a rate of change in distance to a detected light source.
 33. Anautomatic exterior light control as in claim 32 wherein said exteriorlight control signal is an intensity signal.
 34. An automatic exteriorlight control as in claim 32 wherein said exterior light control signalis a horizontal direction signal.
 35. An automatic exterior lightcontrol as in claim 32 wherein said exterior light control signal is avertical direction signal.